Timing modulation system



Patented Slept. 21 194g :Earl -I. Anderson,-Manhasset, 'N. Y., 4assigner to Radio -Corporationfof VAmerica, fa. corporation. of

"Delaware .App1ication-ivramh-1a 1943, serialNo. .41,931.38

This application discloses va new vmetllod off and means :for convertingmodnlaticn frequency energy to timing modulated radioirequency ,energy.' It uses a blockin'gtype ofoscillatcran/d means 'is provided to insure vthat the blocking cycle of the oscillator always Mstarts a`t the same point so that .if the oscillator'is,consideredasa generator only '.(in the absence -off control potential) the generated frequency .is stable. ','Ilhe blocking rate is controllable .and in .my System is controlled by signal currents or other .control potentials. 'The blockingrate is the ,output requency and thus variations in ,the ,blocking rate constitute ircquencyor timingmodulation. ,The blocking rate may |be varied overa wide .range so that .little or 4no frequency multiplication ,is necessary to achieve extensive =.deviation..i.n}.the frequency or timing-of the oscillations. .It. isad vantageous tofuse as .little frequency .multiplication 4as possible in these systems Abecause -frequency .instability is .also .multiplied ,in .the same ratio. If the outputgfrequency. vof .the 1.frequency modulated blocking .oscillator .is .different from that desired for the output v.trecmency5of,.tlf1e.sys tern .the blocking oscillator .output .may .be heterodyned to they desired frequency. .'Ihislneterodyning doesnot multiply. theoscllator instability. Frequency correction means may :be .nsed ,taimprove the oscillator stabilityin `a ,mannerwell known in the art.

In Ydescribing my .invention .reference willbe made .to the attacheddrawings wherein the; single gure illustrates the essential featuresoflazmodulation system arrangement in ,accordance .-with my invention.

In the gure TI is agenerator tube .shown .for the .purpose of .illustration as a triode having .an anode and control grid `regeneratwelycoupled by inductances L and LI. The catholeafihs tube is connected to a point between resistors R3.and.R4 vin shunt to a source of direct current potential to raise the cathode oftheltube'll lsui"-A ciently positive with respect :to-.ground to bias thesame beyond cutoi. vThe grid of .Tlfisconnected ,through inductance .Ll .,tov .a point. on the chargingcircuit for condenser C I. {Ihischargfing circuit comprises `the vresistors RI .and .R2 con-'- nectedwith a positive A,point .of asourceorpotentialsvshownhere as `the source to whichrcsstors RBan'd 'R4 and the anode ,ofjTI Vare connected. Thetube'TZhas its input electrodes-coupled with a .course .of control ypotentials .lll an'd .its anode connected throughresistor'RZ `tothe said source ofjpotential. The'glcondenser'Cl uis shuntedby diode Idevice ld.

A Claims (Cl. 179-1715) "2 The output of the oscillator, fthe operation of whichwill described hereinafter, yis jfehd by rcoupling -con'denserfllandcircuit24 tuned to the generatedfrequency -togtheinput grid y2G of va tube T3. yIhetube '1'.3 vmay be offthe 6K8 or equivalent type llavng a triode section connected -in an ;oscillationgenerating 'circuit includingatnned circuitA 3llgfortheproduction of heterodyning oscillations which kare mixed vinthe tube with the generated oscillations-fed to v,grid 26 lto supply tothe output electrode andoutput circuit -ll- Vthe sum or ydiiiference*frcqiglencyas-desired. `The electron systems in tube-T3 maygbezinV separate .cnvlopes. 'This Output. may Aalso be .supplied to. a mixer'stagein' kEil) Awherein it is 'beat against crystal controlled osc'llationsjand jed 4to a discriminator andfd'etectnr circuit `tovproduce aSrelniency control'potentials which'are fed'to a control electrode of" tube T2 by resistance-52.

iiTubeT'l andthe inductancesL l,and LI form an oscilla-tion circuit which lexceptffvor modincationsdescribed hereinafter would operate in a known' manner to .generate oscillations 4of a 'frequen'cy ndetermine d by the dimensions of :L rand L-l .etc. :Howeveig here the cathode oftube Iil isxraisod` above sroundiby resistorim an. amount inlexcess pf cutoff bias. The charging potential supplied' lcqyR .lA an'dRZ toC'ljfrom the direct c urrent source ,varies with the iflow of ,current throushtube Tzandthis. inturn vares'in .accordanceiwithpthe-appliod oontrolor .modulating potentials applied ltoztho. input .electrodes `.oi ."172- .iAssume'thatth-tube',Tl-is biaseditocotofflontrol voltage is supplied to the `tube "'I.2 andthe current .through .this tubeinoreases. ,As thovoltage .acrossl inoreasesgas .arosultofftho current flowinsgthrouehR i. and. R2 thersbias on thosrid of tcoeTl Lbcoomcslless-negative, ii. decreases untutubell. has su.. .cient Grn .to .startitaoscib late, by .virtue of @the .regenerative .coupling ipolnding Landlfl.- ,'Ihetubo osoillates .during .the time whiolhjit .takesgto .discharge condenserll.,

this'boing a cyolognftheblookins .Circuit .operation.

The discharge path for the condenser'Ql js throughLlgrTl and Ril-#0,5 in shunt. In other words'it-is grid currentto tube-',TI. v-But't'l can discharge vonly to Zero-potential and cannot -be chargedinegatively because as soon asthe cathode ofjdiode I4 becomes negative with respect to ground for-an ap'preciabl-elength ottime-'the Vcurrent'V iiows through diode f4. lngeneral-it can' be saidthatfth-e charge on'Cl cannot becomenegative with respect to ground but that C] discharges tovzeroatfeachcycle'of operation vand at-thistime Bias on the mined by the rate of flow of current into Cl. If,

under operating condition the maximum voltage across Cl is small compared with the voltage at A and Rl is fixed the charging r-ate of C`| is determined by the voltage at A. This rate of flow of .current into C'I is determined or controlled :by the output impedance of tube T2, the latter being de,"y

termined by the control potentials of the grid of tube T2.

As has been explained the rate of flow of current to Cl is controlled by T2 and the rate at which Tl operates is determined by the rate of current iiow into CI (the length of time between cycles of operation of TI is dependent upon the length of time necessary for CI to charge to a voltage which overcomes the bias on TI and thus upon the rate of current fioW into Cl). Thus the output frequency of TI is a function of the modulating frequency applied to T2 and a frequency modulated signal is the result. Circuit 24 is tuned to the center frequency of the output from Tl and is arranged to have the necessary band width to pass the frequency modulated signal.

The repetition rate frequency is then fed to the mixer tube T3 in which it is heterodyned to the desired output frequency. Conventional circuit arrangements may be used in the automatic frequency control circuit including 50 and the control potential is derived by taking some of the output from tube T3 and feeding it to unit 50 wherein it is amplified, changed in frequency, amplitude limited if desired and detected to derive a potential which changes when the mean frequency of the generated Wave changes. This potential is fed out of 50 by way of resistor 52 to the control grid of the tube T2. The polarity of the potential is such that the plate current of tube T2 is changed in a direction to act through the condenser Cl to stabilize or counteract any changes in repetition rate in the blocking oscillator TI other than the changes in accordance with control potentials. The circuits in unit 50 for obtaining the control potential may be arranged as in Crosby U. S. Patents No. 2,279,659 and No. 2,279,660, or as in Seeley Patent No. 2,121,103-

As is usual in frequency modulated transmitters, the radio frequency amplifier stages following the modulated generator are arranged to limit amplitude modulation components in the output so that only frequency modulation is present in the output signal. For example, an amplitude limiter may be included in the coupling between tubes TI and T3 or the limiting action may take place in a stage following tube T3.

I claim:

1. In a system of the class described, an oscillation generator tube having a control electrode biased beyond cutoff, `a condenser and a charging circuit therefor, for applying a positive potential to said control electrode to overcome the said cutoff bias, and a discharge device in shunt to said condenser for preventing a negative charge from being built up thereacross for an appreciable period of time.

2. In a system of the class described, an energy generator tube having a control electrode biased beyond cuto, a condenser and a direct current charging circuit therefor, for applying a positive potential to said control electrode to overcome the said cutoff bias, and a diode connected in shunt to said condenser for preventing a negative charge from being built up thereacross for an appreciable period of time.

3. In a system of the class described, an oscillation generator tube having a control electrode biased beyond cutoff, a condenser and a direct current charging circuit therefor, for applying a potential to said control electrode to overcome the said cutoff bias, to cause said tube to generate energy and discharge said condenser, and a discharge device in shunt to said condenser for preventing a negative charge from being built up thereacross for an appreciable period of time.

4. In a system of the class described, an oscil- V' lation generator comprising a tube having electrodes regeneratively coupled, said electrodes including'a control grid, means for biasing said control grid beyond cutoff, a condenser in a circuit including said control grid, a source of current for charging said condenser to overcome said negative bias whereby said tube becomes conductive to generate pulses and discharge said condenser, an electron discharge tube in shunt to said condenser, and means for controlling the rate of charge of said condenser to correspondingly control the rate of repetition of said charging and discharging of said condenser and as a consequence the rate of repetition of the pulses generated by said tube, comprising an electron discharge device having input electrodes and having output electrodes connected to said source of current, a source of modulation current coupled to the input electrodes of said discharge device, and a frequency stabilizing circuit coupling said generator to an electrode in said device.

5. In a system of the class described, an electron discharge device having an anode-like electrode, a cathode and a control grid coupled in an yalternating current circuit, a direct current bias circuit connected to the grid and cathode of the device for biasing the device to cutoff, a condenser connected between said grid and cathode, an impedance and a source of direct current charging potential in a charging circuit for the condenser, the positive terminal of said source being adjacent to the terminal of the condenser coupled to the control grid so that when current flows through said impedance the charge on said condenser increases to reduce said cutoff bias so that the device becomes operative and the ccndenser discharges, means for controlling the current through said impedance in accordance with sign-als, and a discharge tube in shunt to said condenser to prevent a negative charge from building up thereon. l

6. In `a system of the class described, an electron discharge device having an anode-like electrode, a cathode and a control grid, a circuit regeneratively coupling the anode-like electrode and control grid of the device, a direct current bias circuit connected to the grid and cathode of the device for biasing the device to cutoff, a condenser connected between the grid and cathode of the device, an impedance and a source of direct current charging potential in series with the condenser with the positive end of the source connected to the side of said condenser coupled to the control grid, the arrangement being such that when current flows through said impedance the charge on said condenser increases to reduce said cutoff bias so that the device oscillates by virtue of said regenerative coupling and the condenser discharges, means for controlling the current through said impedance in accordance with signals, and a diode in shunt to said condenser for limiting the extent to which the same can be discharged.

7. In a system of the class described, an electron discharge device having an anode-like electrode, a cathode and a control grid coupled in an alternating current circuit, a direct current bias circuit connected to the grid and cathode of the device for biasing the device to cutoff, a condenser connected between the control grid and cathode, an impedance and a source of direct current charging potential in a charging circuit for the condenser, the positive terminal of said source being adjacent to the terminal of the condenser coupled to the control grid so that when current ows through said impedance the charge on said condenser increases to reduce said cutoff bias so that the device becomes operative and the condenser discharges, a control tube having input electrodes excited by control potentials and having output electrodes connected by said impedance to said source of direct current, and a discharge tube in shunt to said condenser to prevent a negative charge from building up thereon.

8. In a system of the class described, an electron discharge device having an anode-like electrode, a cathode and a control grid coupled in an alternating current circuit, a direct current bias circuit connected to the grid and cathode of the device for biasing the device to cutoff, a condenser connected between the grid and cathode of the device, an impedance and a source of direct current charging potential coupled in series with the condenser with the positive end of the source connected to the side of said condenser coupled to the control grid, the arrangement being such that when current iiows through said impedance the charge on said condenser increases to reduce said cutoff bias so that the device operates and the condenser discharges, means for controlling the flow of direct current through the impedance in accordance with signals, and a discharge tube in shunt to said condenser for limiting the extent to which the same can be discharged.

9. In a system of the class described, an electron discharge device having an anode-like electrode, a cathode and Ia control grid, a circuit regeneratively coupling the anode-like electrode and control grid of the device, a direct current bias circuit connected to the grid and cathode for biasing the device to cutoi, a condenser between said control grid and cathode, an impedance and a source of direct current charging potential in a charging circuit for the condenser. the positive terminal of said source being adjacent to the terminal of said condenser coupled to the control grid of the device, a modulator tube having input electrodes excited by modulating potentials and having output electrodes supplied by direct current through said impedance, the arrangement being such that when current through said impedance to the output electrodes of said tube increases the voltage across said condenser increases to reduce the negative bias on said device so that the device oscillates by virtue of said regenerative coupling and the condenser discharges, connections to the input electrodes of said modulator tube for exciting said input electrodes in yaccordance with signals to control the current through said impedance in accordance with signals, and a diode in shunt to said condenser to limit the extent to which the same can be discharged.

10. In a system of the class described, an electron discharge device having `an anode-like electrode, a, cathode and a control grid coupled in an alternating current circuit, a direct current bias circuit connected to the grid and cathode of the device for biasing the device to cutoff, a condenser connected between said grid and cathode, an impedance and a source of direct current charging potential in a charging circuit for the condenser, the positive terminal of said source being adjacent to the terminal of the condenser coupled to the control grid so that when current flows through said impedance the charge on said condenser increases to reduce said cutoff bias so that the device becomes operative and the condenser discharges, a control tube having input electrodes excited by control potentials and having output electrodes connected through a portion of said direct current circuit to said source of direct current, and a discharge tube in shunt to said condenser to prevent a negative charge from building up thereon.

EARL I. ANDERSON.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number 

